Lean out QF 850 cruise

[cat herder]

Timing curve? Vacuum advance? Ported or manifold vacuum?

[CDN]

At about 2200 your on the man circuit / jets for sure at 2500 so go down 3 jet sizes at the cruise rpm and work up down from there if too lean at WOT then increase PVCR
TSR. at .081. Is not too small id try it forsure it will have the most impact before the mains come

[i82much]

If you were to pull a number completely out of thin air, what percentage of fuel comes from the idle/transition vs main circuit at 2000, 2500, and 3000 rpm? Is it 75/25 at 2000, 50/50 at 2500, 75/25 at 3000? Or is that way off?

[cat herder]

Once the main circuit is up and running the idle circuit turns into an air bleed, and supplies zero fuel from the t-slots & curb idle holes. All these things are interrelated.

[Right hand drive]

Good visualizations

[cat herder]

With the throttle open and the mains active, pressure in the main well, generated by the booster (there's a hint in the name) is lower than the pressure in the throttle bore at the curb idle/t-slot. In a non-divorced idle Holley the idle circuit turns into an air bleed for the main circuit once the boosters are flowing.

tl;dr: That second cute little picture is incorrect.

[Right hand drive]

[cat herder]

If the pressure in the main well, created by the combination of amplification from the booster and the restriction of the main jet, isn't lower than the pressure in the throttle bore, that suggests we can do away with boosters and even venturis altogether! They aren't generating a low enough pressure to be needed for anything and we can get the same result from a straight tube with a discharge hole in the side.

[GTO Geoff]

Surprised by the error above in the coloured [ green ] description of the transfer slot operation. 'Wider T slot = more fuel'.
At idle & until the t/blades are opened far enough off idle to block the top of the T slot, the T slot above the blades acts as an air bleed. If The T slot is wider, more air is admitted to the T slot section above the t/blades, which will lean the mixture.
In general, a performance carb will have a short T slot & an emissions carb will have a long T slot, for the above reason.

[Right hand drive]